Method of heat treating a ti-be alloy



NOV. 7,

Filed Feb. 25, 1959 M- K. M QUILLAN ETA].

METHOD OF HEAT TREATING A T -B ALLOY 2 Sheets-Sheet 1 -406) x a; O

(I) U) u! 5 I 0 v I 2 3 4 5 6. DISTANCE FROM QUENCHED END.(CM S),

FIG. I.

INVENTORS:

Mar/'00 karharmemcquilmji,

Evan William 5 vans, BY W ATTORNEYS.

Nov. 7, 1961 Filed Feb. 25, 1959 M- K. MCQUILLAN ETAL 3,007,824

METHOD OF HEAT TREATING A T B ALLOY 2 Sheets-Sheet 2 Z I o- 0; O

m a/ m E x 0'7 0-8 0-9 0 I-O l-l l-2 l-3 EIGHT A BERYLuuM.

2 INVENTORS:

Mario n Kafh arine McQui/lianfi/ United States Patent Ofilice 3,007,824 Patented Nov. 7, 1961 3,007,824 METHOD OF HEAT TREATING A Ti-Be ALLOY Marion Katharine McQuillan, Birmingham, and Evan William Evans, Halesowen, England, assignors to Imperial Chemical Industries Limited, London, England,

a corporation of Great Britain Filed Feb. 25, 1959, Ser. No. 795,461 Claims priority, application Great Britain Feb. 28, 1958 8 Claims. (Cl. 148-133) This invention relates to alloys.

lthough many titanium alloys have been developed having properties which render them suitable as constructional materials, all sufier from the disadvantage that when in sliding contact under load there is a tendency for the sliding surfaces to seize together, i.e. to gall. A number of proposals have been made with the object of overcoming galling and these include the provision of a hard surface on titanium by induction hardening or by forming a layer of hard material on the surface.

The provision of a hard surface on titanium is also desirable from the point of view of wear resistance, apart from galling, of moving parts.

Titanium-base alloys containing beryllium are known and such alloys have moderate strength and ductility. We have found that certain of these alloys may be heattreated to produce a hard surface.

According to this invention we provide a method of heat-treating a titanium-base alloy containing between 0.6% and 1.2% beryllium, apart from impurities, in which the alloy is heated to a temperature between 820 C. and the upper temperature limit of the beta phase field of the alloy and is then cooled rapidly by quenching in a suitable liquid medium.

The time for which the alloy is heated at the high temperature is not critical; minutes after the attainment of the required temperature is usually sufiicient. Cooling is carried out by quenching in iced brine, water or oil.

As a result of this heat-treatment, the alloys are hardened and strengthened particularly at the surface and the extent to which this effect occurs is independent of the period of time for which the material is held at the required temperature but dependent on the cooling rate from that temperature.

A high rate of cooling, such as by quenching in iced brine or in water produces a high degree of hardening on the surface. With slower rates of cooling, as by oil quenching, lower hardness of the surface results. In material other than thin sheet the interior of the metal (hereinafter referred to as the core) remains comparatively soft. In thin sheet, the depth of the hardening may be such as to penetrate through the entire thickness of the material, though in most instances the actual hardness at the centre will be less than that of the surface.

Heat-treatments carried out after hardening have shown that no loss of hardening is likely to occur if the hardened alloy is heated in service to temperatures less than 300 C. Even 5 hours heating at 400 C. produces softening of less than 50 points on the Vickers scale.

In order to illustrate the invention a titanium-0.8% beryllium alloy was fabricated in the form of a bar of Vs inch diameter and 2 inches long and was heated at 980 C. for ten minutes being then quenched into water. Hardness measurements made on a cross section of the bar showed the presence of a surface layer of hardness 500 Vickers diamond pyramid numeral whereas the core had a hardness of 197 Vickers diamond pyramid numeral. Before heat-treatment, hardness values of specimens of alloys containing 0.8% beryllium were in the range 228 to 241 Vickers diamond pyramid numeral.

In order further to illustrate the invention a test piece (of similar composition to that just described) was heated at 980 C., which is between the eutectoid and eutectic temperatures, for ten minutes, and one end of the test piece was quenched in water at 0 C., the remainder being allowed to cool in air. Hardnesses were determined at points along its length and the variation of hardness with distance along the bar is shown in FIGURE 1 of the accompanying drawings. This shows that, at the quenched end, there is a narrow zone having a high hardness value which falls ofi rapidly at first and then at a decreasing rate.

Hardness tests on titanium-beryllium alloys containing different amounts of beryllium are shown in graphical form in FIGURE 2 of the accompanying drawings. The effects on the core (lower curve) and on the surface (upper curve) of heating to 980 C. and quenching small test pieces into iced brine are shown and it will be observed that the greatest surface hardness is obtained over a small range of composition.

In Table I are given tensometer test results for the 1.0% beryllium alloy heat-treated in rod form and machined to test piece size. These values indicate the strength and ductility of the metal below the hard surface layer.

It will be seen from the graphs and from Table I that alloys of titanium which have a high surface hardness and good strength and ductility in the core may be produced by the method according to the invention.

If required, however, toughness and ductility can be further improved with some loss in hardness by heattreating the hardened mateiial at temperatures in the range 400 to 820 C., as for instance an alloy containing 0.8% beryllium heated for 4 hours at 600 C. after a hardening treatment of 10 mins. at 1000 C. followed by an iced brine quench, which had a U.T.S. of 50.8 t.s.i. and elongation of 11%.

We claim:

1. A method of heat treating a titanium-based alloy consisting essentially of 0.6% to 1.2% beryllium, balance titanium, apart from impurities which comprises heating the alloy to a temperature between about 980 C. and the upper temperature limit of the beta phase field of the alloy, and then cooling rapidly by quenching in a suitable liquid medium, whereby the surface hardness of said alloy is increased to greater than about 350 points on the Vickers scale and the core hardness is increased to greater than about 200 points on the Vickers scale.

2. A method of heat treating as set forth in claim 1 in which the temperature to which said alloy is heated is about 980 C.

3. An article having a substantially hard surface and a core softer than said surface consisting essentially of about 0.6 to 1.2% beryllium, balance titanium apart from impurities and heat treated according to the method of claim 1.

4. A method of heat treating a titanium-based alloy consisting essentially of about 0.8% beryllium, balance titanium, apart from impurities, which comprises heating the alloy to a temperature between about 980 C. and

the upper temperature limit of the beta phase field of the alloy, and then cooling rapidly by quenching in a suitable liquid medium, whereby the surface hardness of said alloy is increased to greater than about 350 points on the Vickers scale and the core hardness is increased to greater than about 200 points on the Vickers scale.

5. A method as set forth in claim 4 in which the temperature to which said alloy is heated is about 980 C.

6. A method as set forth in claim 4 in which the alloy is quenched in water.

7. A method as set forth in claim 4 in Which the alloy is quenched in iced brine.

8. A method as set forth in claim 4 including heating said alloy, after quenching, to a temperature in the range of 400 C. to 820 C., whereby the toughness and ductility of the alloy is improved for a period of time.

References Cited in the file of this patent UNIT ED STATES PATENTS Crossley July 9, 1957 Crossley July 30, 1957 OTHER REFERENCES AF Technical Rept. No. 6218, June 1950, Research and Development on Titanium Alloys, Battelle Memorial Institute, Columbus, Ohio. Pages 28 and 29. 

1. A METHOD OF HEAT TREATING A TITANIUM-BASED ALLOY CONSISTING ESSENTIALLY OF 0.6% TO 1.2% BERYLLIUM, BALANCE TITANIUM, APART FROM IMPURITIES WHICH COMPRISES HEATING THE ALLOY TO A TEMPERATURE BETWEEN ABOUT 980*C. AND THE UPPER TEMPERATURE LIMIT OF THE BETA PHASE FIELD OF THE ALLOY, AND THEN COOLING RAPIDLY BY QUENCHING IN A SUITABLE LIQUID MEDIUM, WHEREBY THE SURFACE HARDNESS OF SAID ALLOY IN INCREASED TO GREATER THAN ABOUT 350 POINTS ON THE VICKERS SCALE AND THE CORE HARDNESS IS INCREASED TO GREATER THAN ABOUT 200 POINTS ON THE VICKERS SCALE. 